Crystalline molecular sieves have a 3-dimensional, four-connected framework structure of corner-sharing [TO4] tetrahedra, where T is any tetrahedrally coordinated cation. Among the known forms of molecular sieve are aluminosilicates, which contain a three-dimensional microporous crystal framework structure of [SiO4] and [AlO4] corner sharing tetrahedral units, aluminophosphates (ALPOs), in which the framework structure is composed of [AlO4] and [PO4] corner sharing tetrahedral units and silicoaluminophosphates (SAPOs), in which the framework structure is composed of [SiO4], [AlO4] and [PO4] corner sharing tetrahedral units.
Molecular sieves have been classified by the Structure Commission of the International Zeolite Association according to the rules of the IUPAC Commission on Zeolite Nomenclature. According to this classification, framework-type zeolite and zeolite-type molecular sieves, for which a structure has been established, are assigned a three letter code and are described in the Atlas of Zeolite Framework Types, 5th edition, Elsevier, London, England (2001), which is herein fully incorporated by reference.
Molecular sieves are typically described in terms of the size of the ring that defines a pore, where the size is based on the number of T atoms in the ring. Other framework-type characteristics include the arrangement of rings that form a cage, and when present, the dimension of channels, and the spaces between the cages. See van Bekkum, et al., Introduction to Zeolite Science and Practice, Second Completely Revised and Expanded Edition, Volume 137, pages 1-67, Elsevier Science, B. V., Amsterdam, Netherlands (2001).
In general, molecular sieves can be divided into small, medium and large pore materials. Thus small pore molecular sieves typically have pores defined by a ring of no more than 8 T atoms and have an average pore size less than about 0.5 nm (5 Å). Medium pore molecular sieves typically have pores defined by a ring of 10 T atoms and have an average pore size about 0.5 to 0.6 nm (5 to 6 Å), whereas large pore materials have pores defined by rings of 12 or more T atoms and a pore size greater than 0.6 nm (6 Å).
Crystalline molecular sieves, as exemplified by zeolites and (metallo)aluminophosphates, are commercially important materials for petroleum processing and petrochemical applications. Because each unique structure type offers new potential for applications in catalysis and separations, there has been sustained research effort, both in industry and academia, for their discovery.
Many molecular sieves are synthesized in the presence of an organic directing agent, such as an organic nitrogen compound. For example, it is known from, for example, U.S. Pat. No. 6,680,278 that a crystalline silicoaluminophosphate molecular sieve of the CHA framework type (a small pore material), can be synthesized in the presence of an organic directing agent mixture comprising tetraethylammonium cations and one or more dimethylamino moieties selected from one or more of N,N-dimethylethanolamine, N,N-dimethylpropanolamine, N,N-dimethylbutanolamine, N,N-dimethylheptanolamine, N,N-dimethylhexanolamine, N,N-dimethylethylenediamine, N,N-dimethylbutylenediamine, N,N-dimethylheptylenediamine, N,N-dimethylhexylenediamine 1-dimethylamino-2-propanol, N,N-dimethylethylamine, N,N-dimethylpropylamine, N,N-dimethylpentylamine, , N,N-dimethylhexylamine and N,N-dimethylheptylamine. Other organic directing agents that have been used in the synthesis of CHA framework type materials include isopropylamine or di-n-propylamine triethylamine, cyclohexylamine, 1-methylamidazole, morpholine, pyridine, piperidine, diethylethanolamine, and N,N,N′,N′-tetraethylethylene diamine.
It is also known to use fluoride-containing compounds, such as hydrogen fluoride, as mineralizing agents in molecular sieve synthesis. For example, EP-A-337,479 discloses the use of hydrogen fluoride in water at low pH to mineralize silica in glass for the synthesis of ZSM-5. In addition, U.S. Patent Application Publication No. 2003/0231999 published Dec. 18, 2003 and incorporated herein by reference, discloses that aluminophosphate or silicoaluminophosphate molecular sieves having the CHA framework type can be synthesized in the presence of fluoride ions using the dimethylamino compounds disclosed in U.S. Pat. No. 6,680,278 as directing agents. However, fluoride-based syntheses pose environmental problems in that they use hydrogen fluoride in the synthesis medium and/or produce hydrogen fluoride on calcination to remove the organic directing agent from the molecular sieve product.
Currently, an entirely rational approach that leads to the synthesis of unique framework materials is not available, due to the fact that all crystalline microporous materials are metastable phases and they are kinetic products. Their discovery is therefore often serendipitous.
Our research has led to two findings: that 4-DMAPy can direct the synthesis of low-silica SAPO-CHA in a low fluoride or fluoride-free medium and in the presence of colloidal SAPO-34 seeds; and, from parallel experiments, that without SAPO-34 seeds, use of the same directing agent under no- or low-fluoride , conditions unexpectedly led to the production of the present large pore aluminophosphate designated EMM-8.
According to an article in the Chemical Journal of Chinese Universities, Vol. 22, No. 10, pages 192-195, dated October 2001, DMAPy has been used as a template in the synthesis of NK-101, an aluminophosphate. However, FIG. 1 provides a comparison of the X-ray diffraction pattern of NK-, 101 with that of EMM-8 and it is apparent from this comparison that the material of the invention is different from NK-101. In particular, in the X-ray diffraction pattern of NK-101, the most prominent diffraction peaks are at 2-theta values of approximately 17° and 19°, whereas these peaks are not present in the X-ray diffraction pattern of EMM-8.
In an article entitled “SSZ-51—A New Aluminophosphate Zeotype: Synthesis, Crystal Structure, NMR, and Dehydration Properties”, published on the Web by the American Chemical Society on Jun. 23, 2004, Morris et al. report that they have synthesized and solved the structure of a new aluminophosphate zeotype framework structure, SSZ-5 1, having the empirical formula Al4(PO4)4F.C7N2H11.0.5H2O. The synthesis employs 4-dimethylaminopyridine , as a structure directing agent and requires the presence of fluoride ion as a mineralizing agent. The structure of SSZ-51 is said to be closely related to that of SAPO-40, an AFR framework type material, and to contain intersecting channels defined by 8- and 12-membered ring windows. It appears that SSZ-51 is isostructural with EMM-8.
U.S. Patent Application Publication No. 2003/0232718 published Dec. 18, 2003 discloses the synthesis of silicoaluminophosphate molecular sieves using templates that contain at least one dimethylamino moeity. The use of such templates is said to result in good quality SAPO molecular sieves of CHA framework type.
EP-A-0 324 082 discloses the synthesis of non-zeolite molecular sieves by contacting alumina or silica-alumina bodies with a liquid reaction mixture containing a reactive source of phosphorus and an organic templating agent.